1. Field of the Invention
The present invention relates to a method for controlling a cooling fan to dissipate heat generated by a CPU, a power supply, and other electrical components in a computer system, and more particularly to a control method for reducing the noise generated by the cooling fan.
2. Background of Related Art
Generally, a computer system comprises a board with various LSI chips such as a CPU mounted thereon, a storage device such as a hard disk, a battery device, and input/output devices, each of which is known to generate heat as each operates in a computer. For some electrical components, such as a CPU, a temperature range is often indicated by specifications which set a temperature range indicative of satisfactory and/or optimum performance (hereinafter, as used herein, this temperature and range may also be referred to as xe2x80x9crated temperaturexe2x80x9d), and often a cooling fan is typically provided in conjunction with electrical components in a computer system to keep the temperature in the system within the rated temperature.
Certain methods for controlling the rotational frequency of such cooling fans for heat dissipation are known in the art and include:
1) Scheme 1: Fan Control at a Constant Rotational Frequency
When a computer system is powered on, heat generating objects begin to operate, and in turn, often generate heat due to their operation. Examples of these xe2x80x9cheat generating objectsxe2x80x9d include but are not limited to a CPU, a hard disk, a power supply, etc.
With particular reference to a CPU, it is known that the amount of heat generated by an operative CPU varies widely depending on the operating conditions, the temperature of the CPU, and the temperature in the housing. For instance, it is known that as a CPU operates, heat is generated and dissipated into the computer housing environment, where the total heat present within a computer housing increases and the temperature within the housing rises accordingly. It is known to offset such a temperature rise by air-cooling of a heat sink (radiation plate) attached on the top of the CPU package, and also through discharging the heated air in the housing to the outside by rotating an attached fan at a constant rotational frequency. Since the amount of heat generated within the housing and the required cooling capacity are in a certain relation, in this scheme 1, the required cooling capacity (also used as the rotational frequency of the fan, herein) is determined assuming a condition in which all the components operate at their maximum heat generation capacity, such that the fan is then driven constantly at the maximum rotational frequency.
2) Scheme 2: Fan Control by Means of a Temperature Sensor
In this second scheme, the rotational frequency of the fan is controlled using the temperature value obtained by a temperature sensor attached to the object to be cooled. That is, a specific rotational frequency is predetermined corresponding to a certain temperature, and the cooling fan is controlled in response to the temperature value obtained from the temperature sensor to maintain the predetermined rotational frequency.
In this second scheme, for instance, the rotational frequency of the fan is controlled in either of: (a) two steps: a stop and a constant rotation steps, or (b) in three steps: a stop, a low speed rotation, and a high speed rotation steps; and the rotational frequency of the fan is switched to a specific value for a set temperature threshold value. However, when the rotational frequency of the fan is controlled in a few steps, it is typically not possible to control the rotational frequency of the fan precisely to a minimum rotational frequency corresponding to the heat generation level of the heat source at each moment.
In the conventional scheme 1, the rotational frequency of the fan is determined assuming a maximum temperature and heat generation of the object to be cooled, and the fan is driven constantly at that rotational frequency; therefore, the fan tends to be driven continuously at a rotational frequency exceeding the cooling capacity normally required at that moment. Therefore, in this second scheme, the rotational frequency of the fan would increase with the increase of heat generation resulting from recent higher standard of specifications of each component, and also speed-up of the fan rotational frequency would be facilitated by the downsizing of the fan itself associated with the downsizing of the computer system. As a consequence, given such tendency, it has become an increasing problem in maintaining a quiet work environment, such as offices. In the conventional scheme 2, the rotational frequency can be lowered on average compared to scheme 1, but when the rotational frequency is switched, the change of rotational frequency itself may also become a noise source which causes one an uncomfortable feeling. This will be further explained using FIG. 1.
FIG. 1 illustrates the relation between the temperature change in the object to be cooled and the rotational frequency of the fan in the conventional fan control schemes.
From FIG. 1, the abscissa of each graph represents a time axis. The ordinate of the upper diagram shows how the temperature in the object to be cooled changes in each conventional control scheme. The ordinate of the lower diagram shows how the rotational frequency of the fan changes in each conventional control scheme. The hatched area in the lower diagram represents the range of the rotational frequencies that would cause uncomfortable feeling of a human. As already described, scheme 1 has disadvantages in that the objects to be cooled tend to be cooled more than is actually needed, and the rotating noise of the fan tends to be annoying at most all times. On the other hand, in scheme 2 (an example of two-step cooling is shown here for simplicity), a continuous swelling noise may be generated in the vicinity of the threshold values since the rotational frequency of the fan is constantly switched between specific values.
The method for controlling a cooling fan by means of a temperature sensor as shown in scheme 2 is known in art and more particularly from Published Unexamined Japanese Patent Application No. 6-4294 (xe2x80x9cVariable Revolution Controlled Fanxe2x80x9d) or Published Unexamined Japanese Patent Application No. 9-250489 (xe2x80x9cRotational Frequency Control Apparatus for Cooling Fanxe2x80x9d), each of which is incorporated herein by reference.
The former discloses a method for controlling a rotational frequency of a fan utilizing the fuzzy theory based on temperature value detected by a temperature sensor, and the latter discloses a method in which cooling fans and temperature sensors are placed at multiple locations and the rotational frequency of the cooling fan is controlled based on temperature value obtained by the temperature sensors at multiple points. However, both of these Published Applications focus on providing stable cooling and provide a method of switching the control mode of fan at predetermined specific rotational frequencies in accordance with detected temperature value, and therefore, neither discloses a more practical method to realize a fan control at a low noise level while maintaining sufficient cooling performance concurrently.
The present invention overcomes the above described problems and it is an object of the present invention to realize noise reduction of a cooling fan by controlling the fan rotation to a minimum rotational frequency in accordance with the specification and performance of the heat source.
It is another object of the present invention to control a cooling fan to a minimum allowable rotational frequency within a rated temperature range of the object to be cooled, thereby controlling the internal temperature of a computer system in such a way to minimize noise generation.
It is a further object of the present invention to provide a low noise output and an effective method for controlling a cooling fan based on a relatively simple and low-cost configuration.